Synthesis And Catalytic Properties Of Catalysts Based On Metal Cobalt And Vanadium

The rapid depletion of fossil fuels and its negative influence on the global environment have seriously hindered economic and social development and even threaten the survival of human beings around the world.Hydrogen,high-energy and eco-friendly,is regarded as one of the most promising energy.The electrochemical and photocatalytic water splitting is the acknowledged promising method to produce high-purity hydrogen and oxygen,which can be widely realized with the presence of industrial catalytic facility.Generally speaking,a complete overall water splitting system can be divided into two half-reactions,including hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?,while such sluggish reaction kinetics and high reaction barriers during electrolysis procedure require highly active catalysts to decrease the overpotential and increase the reactive rate.Noble metal?e.g.,Pt,Ru,and Ir?based catalysts exhibit efficient catalytic activity,while the large-scale application is restricted due to their high economic-cost and low earth-storage.Therefore,developing non-noble and mass-produced bifunctional catalysts for overall water splitting is a pressing and challenging task.In this paper,we have prepared the Co or V based compounds and invested their electrocatalytic activity for water splitting.The main contents of the research are listed as follows:Part 1:Heterogeneous cobalt phosphides nanoparticles anchored on carbon cloth realizing the efficient hydrogen generation reaction.Intrinsic activity modifying of electrocatalysts is crucial to realizing the excellent catalytic performance towards hydrogen evolution reaction.Herein,we demonstrate a highly efficient electrocatalyst based on heterogeneous cobalt phosphides nanoparticles.The morphology,structure and composition of the catalyst were characterized by X-ray diffraction,X-ray photoelectron spectroscopy,scanning electron microscopy and transmission electron microscopy.The hydrogen evolution performance of heterogeneous cobalt phosphide nanoparticles was measured in an acidic electrolyte solution.As a consequence,the as-prepared heterogeneous cobalt phosphides nanoparticles supported on carbon cloth exhibit impressive electrocatalytic activity,which only acquire a small overpotential of 90 mV at a current density of 10mA cm^-2,and present a low Tafel slope(67.9 mV dec^-1),a large exchange current density(0.58 mA cm^-2)as well as good durability.Therefore,this work provides a favorable guidance for exploring executable strategies to improve catalyst activity.Part 2:One-step solvothermal synthesis of amorphous CoVO nanoparticles for efficient oxygen evolution.In this work,amorphous cobalt vanadate nanoparticles?a-CoVO?were successfully synthesized by one-step solvothermal method,and high-efficiency oxygen evolution reaction was achieved in an alkaline electrolyte solution.The solvothermal method uses water and ethylene glycol as solvents to synthesize highly crystalline bulk cobalt vanadate?c-CoVO?and amorphous cobalt vanadate nanoparticles?a-CoVO?.The high viscosity of ethylene glycol as a solvent ensures the successful preparation of amorphous cobalt vanadate nanoparticles.The amorphous cobalt vanadate nanoparticles can expose more active sites,and also promote sufficient contact of the catalyst itself with the electrolyte solution,which can greatly improve the oxygen evolution reaction activity of the catalyst.When amorphous cobalt vanadate nanoparticles?a-CoVO?are subjected to oxygen evolution under alkaline conditions,a-CoVO exhibits a lower overpotential,a smaller Tafel slope,and good catalytic stability.This work has confirmed that cobalt vanadate nanomaterials have good catalytic activity in oxygen evolution reaction,which provides a reference for exploring more efficient electrochemical cracking water catalysts.Part 3:In suit Construction of Cobalt-vanadium Based Nanocomposites as Bifunctional Catalysts for Efficient Overall Water Splitting.Designing the low-cost and high-active bifunctional catalysts for overall water splitting has attracted increasing research interest.Herein,we report the efficient overall water splitting performance for the cobalt-vanadium bimetal-based nanocomposites.The nanocomposites are synthesized through a one-step hydrothermal method,in which the cobalt species is introduced to the lepidocrocite VOOH.It is proved that the added cobalt species will form cobalt vanadium oxide in the preparation process.The targeted catalyst(denoted as Co_0.2-VOOH)exhibits a unique layered structure.As a consequence,the targeted bifunctional catalyst can achieve the current density of 10 mA cm^-2 at the overpotentials of 210 mV for water oxidation and 130 mV for hydrogen generation,respectively.Notably,it only requires the low cell voltages of 1.57 and 1.74 V to drive the catalytic current densities of 10 and 100 mA cm^-2 during water splitting process.This work significantly indicates that the cobalt-vanadium based materials are promising alternatives for overall water splitting.